Sure, for any given focal length the angle of coverage will vary between FX and DX. Doesn’t SB800 already vary its angle of coverage with the change in focal length with a zoom lens (I believe that the D40 manual says as much, p. 99). So if the angle of flash coverage can/does change with focal length why not with sensor size?

Beat

Currently the zoom reflector on SB-800 / 600 still work in FX mode: they read the zoom setting on the lens and move to the same value causing a too wide beam spread.So yes it does make sense but it’s the DX that would benefit not the FX…